Process for the hydrodimerization of acrylic acid derivatives

ABSTRACT

IN THE HYDRODIMERIZATION OF ACRLONITRILE AND LOWER ALKYL-SUBSTITUTED ACRYLONITRILES BY CONTACTING THE NITRILES WITH AN ALKALI METAL AMALGAM FOR OBTAINING THE RESPECTIVE ADIPONITRILES, THE IMPROVEMENT OF USING IN THE REACTION A SOLVENT MEDIUM WHICH IS AT LEAST PARTLY WATER-MISCIBLE AND DISSOLVE BOTH THE STARTING COMPOUNDS AND THE HYDRODIMERS, THE AMOUNTS OF THE REACTANTS BEING OF THE ACYLIC ACID DERIVATIVES 5-20% BY WEIGHT, OF WATER 5-30% BY WEIGHT, AND OF A FREE QUATERNARY AMMONIUM BAS 0.0015% BY WEIGHT, THE DEGREE OF ALKALINITY BEING THAT GENERATED BY THE REACTION. TOGETHER WITH THE METNTIONED ADIPONITRILES, ALKALI METAL HYDROXIDE IS RECOVERED AS BYPRODUCT-.

United States Patent ce Int. (11. Cine 121/26 US. Cl. 260-4653 A 6 Claims ABSTRACT OF THE DISCLOSURE In the hydrodimerization of acrylonitrile and lower alkyl-substituted acrylontriles by contacting the nitriles with an alkali metal amalgam for obtaining the respective adiponitriles, the improvement of using in the reaction a solvent medium which is at least partly water-miscible and dissolves both the starting compounds and the hydrodimers, the amounts of the reactants being of the acrylic acid derivatives 20% by weight, of water 5-30% by weight, and of a free quaternary ammonium bas 0001- 5 by weight, the degree of alkalinity being that generated by the reaction. Together with the metntioned adiponitriles, alkali metal hydroxide is recovered as byproduct.

This application is a continuation of Ser. No. 702,821, filed Feb. 5, 1968, now abandoned.

This invention relates to the hydrodimerization of acrylic acid derivatives, which term, in the context of the present invention, means arcylonitrile, lower-alkyl acrylonitriles as well as lower-alkyl esters and amides of acrylic acid to form the corresponding functional derivatives of adipic acid.

The dimerization may be one in which two molecules of the same acrylic acid derivative are combined into a symmetric adipic acid derivative (homodimerization) or one in which two different acrylic acid derivatives are combined into asymmetric adipic acid derivatives having different functional groups at both ends of their chain hetero-dimerization) The adipic acid derivatives that can be prepared by the process according to the invention are suitable for use as reactants in the manufacture of polyamides from which man-made fibers and plastics in general can be manufactured.

The hydrodimerization of acrylic acid derivatives is known. The processes used, or proposed for use, up to now are classifiable into two groups:

(a) Electrolytic hydrogenation (b) Reduction by alkali metal amalgam The electrolytic processes require special electrolytic cells and the control of the operation is technically complicated.

The amalgam processes, on the contrary, are easier and simpler to perform, and under certain conditions provide considerable technical advantages over electrolytic hydrogenation.

In both cases the yield, calculated on the weight of the acrylic acid derivative used as a starting material, is affected by the formation of by-products, which, as a rule, are undesired. This happens on the one hand by the reduction of the acrylic acid derivatives without dimerization, whereby propionic acid derivatives are formed, and on the other hand by the formation of polymers.

This invention has the object to provide an improvement of the amalgam hydrodimerization processes with a view 3,686,269 Patented Aug. 22, 1972 to achieving good yields of dimers and this in a much simpler way than the one in which the amalgam process could be carried out up to now.

With a view to making the hydrodimerization of acrylionitrile by means of alkali metal amalgam more efiicient it has been suggested to add certain salts to the reaction mixture, among them quaternary amomnium salts. As disclosed in the literature this particular process is carried out with permanent control of the pH of the reaction mixture in the range 7 to 10. The pH control is achiever by the slow addition of an acid, by bubbling CO gas or by addition of a large excess of buifer which is consumed by the alkali liberated in the reaction. It is stated in previous publications that at high pH values, undesired by-products such as oxydipropionitrile are formed and that it is therefore preferable to work in neutral media. This known process has the double disadvantage that it requires a high proportion of the relatively costly quaternary ammonium salts, of the order of 10 to 40% of the reaction mixture, which will have to be recovered from the spent reaction mixture for recycling, and that the alkali metal hydroxide liberated from the amalgam in the course of the reaction is lost as a virtually valueless salt which, in addition, forms an inconvenient sediment in the interphase between the mercury and the reaction liquor, which has to be removed.

The present invention aims at avoiding these drawbacks.

The invention consists in a process for the hydrodimerization of acrylic acid derivatives selected from the group consisting of acrylonitrile, lower alkyl acrylonitriles, lower alkyl esters and amides of acrylic acid by their reaction with an alkali metal amalgam which comprises carrying out the reaction in a non-polar, at least partly water-miscible solvent medium containing a free quaternary ammonium base and water, the process being performed without pH control at the degree of alkalinity generated by the reaction.

Suitable solvents for the process are, for example, ethers, such as tetrahydrofuran, dioxane, dimethoxyethane or diglyme, (diethyleneglycol dimethyl ether) or alcohols such as t-butanol, always on condition that they are at least partially miscible with water, while others, e.g. ethers, that are substantially immiscible with water, such as diethyl ether, are unsuitable. Among the alcohols, tertiary alcohols containing not more than 6 carbon atoms per hydroxyl group are preferred, while the use of primary and secondary alcohols tends to favour the forma tion of undesired by-products.

Quaternary ammonium bases suitable for the purposes of the present invention are those of the formula where R R R and R are the same or different alkyl, cycloalkyl, aryl or aralkyl, radicals. The number of carbon atoms of these radicals may be chosen within wide limits, but the less bulky groups are preferred, since the extension of the number of carbon atoms in these groups merely dilutes the active sites of the quaternary bases. Quaternary bases of more than single functionality, as far example, diquaternary bases, are also very useful for use in the process of the invention. As a rule, the quaternaty ammonium base is preferably used in a concentration of 0.001 to 5%, preferably 0.01 to 0.2%, by weight of the reaction mixture (exclusive of the alkali metal amalgam).

Although the explanation of the reaction mechanism is not a part of the invention, it is believed that the role of the water in the medium is to provide the protons necessary for the hydrogenation occurring in the dimerization process. The optimum concentration of the proton-donating component in the reaction medium is between 5% and 30% by weight, while the concentration of the acrylic acid derivative used as a starting material is preferably between 5% and 20% by weight. The use of higher concentrationsof, for example, acrylonitrile may cause the formation of undesirable by-products, such as oligomers or polymers.

Though any alkali metal amalgam can be used in the process of the invention, sodium amalgam seems to produce the best results. The alkali metal amalgam is readily available as an intermediate in the electrolytic production of chlorine and alkali.

The process according to the invention can be carried out within a Wide temperature range, from about -10 C. to about 30 C. Good results are achieved at temperatures of about C. It is advisable strongly to agitate the reaction mixture in the course of the hydrodimerization.

It is an advantage of the method according to the invention that no acid is consumed and that the alkali hydroxide formed can subsequently be recovered from the reaction medium as a valuable by-product. Thus, under another aspect the invention consists in the simultaneous production of adipic acid derivatives and alkali metal hydroxide. Moreover, the amounts of quaternary base here required for the process are so small that the base need not be recovered from the reaction products though the recovery is possible.

The invention is illustrated by the following examples to which it is not limited:

EXAMPLE 1 10 g. of acrylonitrile, 24 g. of water and 0.5 g. of a 40%-by-weight aqueous solution of benzyl trimethyl ammonium hydroxide were dissolved in 65 cc. of diglyme (diethyleneglycol dimethyl ether). The solution was added to 2 kg. of sodium amalgam (sodium concentration 0.3% by weight). The mixture was stirred vigorously for minutes in an ice bath. The depleted amalgam was separated from the reaction mixture which, thereafter, consisted of two phases. The bottom phase was a concentrated aqueous sodium hydroxide solution containing 5.5 g. of NaOH. The top phase was diluted with water and extracted with methylene chloride. The reaction product was analyzed by gas chromatography; it contained 8.2 g. of adiponitrile, 0.6 g. of propionitrile and 0.5 g. of unreacted acrylonitrile. This amounted to an 86% adiponitrile yield and a 6.3% propionitrile yield based on the reacted acrylonitrile. The metal conversion yield was 90%.

The products were separated from the extract by distillation of the low boiling fractions at atmospheric pressure, and of the adiponitrile at a reduced pressure of 20 mm. Hg (B.P. 180-182).

EXAMPLE 2 g. of acrylonitrile, 10 g. of Water and 0.05 g. of a 40%-by-weight aqueous solution of benzyl trimethyl ammonium hydroxide were dissolved in 80 cc. of diglyme. The solution was reacted with sodium amalgam in the manner described in Example 1. The product contained 6.5 g. of adiponitrile, 0.4 g. of propionitrile and 1.8 g. of unreacted acrylonitrile, i.e. a 79% yield of adiponitrile and a 4.9% yield of propionitrile. The metal conversion was 86%.

EXAMPLE 3 5 g. of acrylonitrile, 10 g. of water and 0.4 g. of a 40%- by-Weight aqueous solution of benzyl trimethyl ammonium hydroxide were dissolved in 80 cc. of tetrahydrofuran. The solution was treated as described in Example 1. The reaction product contained 90% of adiponitrile and 5% of propionitrile. The metal conversion yield was 90%.

EXAMPLE 4 10 g. of acrylonitrile, 20 g. of water and 0.5 g. of a 40%-by-weight aqueous solution of benzyl trimethyl am- 4 monium hydroxide were dissolved in 70 cc. of t-butanol. The solution was treated as described in Example 1. The product contained 70% of adiponitrile and 20% of propionitrile. The metal conversion yield was 85%.

EXAMPLE 5 10 g. of acrylonitrile, 10 g. of water and 0.4 g. of a 40%-by-weight aqueous solution of tetrabutyl ammonium hydroxide were dissolved in cc. of dioxane The solution was reacted with sodium amalgam as described in Example 1. The product contained 50% of adiponitrile and 19 of propionitrile. The metal conversion yield was EXAMPLE 6 10 g. of acrylonitrile, 10 g. of water and 0.5 g. of a 40%-by-Weight aqueous solution of trimethyl phenyl ammonium hydroxide were dissolved in 80 cc. of dioxane. The solution was reacted with sodium amalgam as described in Example 1. The product contained 91% of adiponitrile. The metal conversion yield was 92%.

EXAMPLE 7 10 g. of acrylonitrile, 10 g. of water and 0.5 g. of a 40%-by-weight aqueous solution of trimethyl cetyl ammonium hydroxide were dissolved in 80 cc. of dioxane. The solution was reacted with sodium amalgam as described in Example 1. The product contained 75% of adiponitrile and 3.5% of propionitrile. The metal conversion yield was 88%.

EXAMPLE 8 10 g. of acrylonitrile, 20 g. of water and 1.0 g. of a 75 %-by-weight aqueous solution of dicoco dimethyl ammonium hydroxide were dissolved in 70 cc. of diglyme. The solution was reacted with sodium amalgam in the manner described in Example 1. The product contained 76% of adiponitrile and 4% of propionitrile. The metal conversion yield was The quaternary base used in this example was prepared from a product known as dicoco-dimethyl ammonium chloride made by Armor Industrial Chemical Company, Chicago, the coco radicals being obtained from alcohols prepared from coco oil.

EXAMPLE 9 10 g. of acrylonitrile, 10 g. of water and 0.4 g. of a 50%-by-weight aqueous solution of triethylene-diamine dimetho hydroxide (1,4-dimethyl 1,4 diazonia-bicyclo (2,2,2) octane dihydroxide) were dissolved in 80 cc. of tetrahydrofuran. The reaction was carried out as described in Example 1. The products contained 90% of adiponitrile and 2.5% of propionitrile. The metal conversion yield was 94%.

EXAMPLE 10 10 g. of l-methyl acrylonitrile, 10 g. of water and 0.5 g. of a 40%-by-Weight aqueous solution of benzyl trimethyl ammonium hydroxide were dissolved in 80 cc. of diglyme. The solution was reacted with sodium amalgam as described in Example 1. The reaction was stopped after 50% of the monomer had reacted. The product contained 62% of 2,5-dimethyl adiponitrile and 20% of isobutyronitrile. The metal conversion yield Was 85%.

What is claimed is:

1. In a process for the hydrodimerization of an acrylonitrile starting material selected from the group consisting of acrylonitrile and l-methyl-acrylonitrile to produce adiponitrile and 2,S-dimethyl-adiponitrile, respectively, by contacting an alkali metal amalgam with a liquid hydrodimerization medium containing said starting material and water, the improvement which comprises that said liquid dimerization medium essentially consists of the starting material, water, a free quaternary ammonium base being N,N-dimethyl-triethylene-diammonium dihydroxide or a compound of the formula wherein R and R each represent lower alkyl, R represents alkyl of from to 18 carbon atoms and R is a member selected from the group consisting of alkyl of from 1 to 18 carbon atoms, phenyl and benzyl, and a water-miscible solvent for said starting material and the hydrodimers, in which medium the proportion of the starting material is of from 5 to 20% by weight, the proportion of water is of from 5 to 30% by weight, the proportion of the free quaternary ammonium base is of from 0.001 to 5% by weight, the balance consisting essentially of the watermiscible solvent, said solvent being selected from the group consisting of tetrahydrofuran, dioxane, dimethoxyethane, diethyleneglycol dimethyl ether and tert. butanol, the dimerization being carried out at the degree of alkalinity which corresponds to that generated by the decomposition of the amalgam in the course of the reaction.

2. A process according to claim 1, wherein the quaternary ammonium base is used in a proportion of 0.01 to 0.2% by weight of the solvent medium.

3. A process according to claim 1, wherein the quaternary ammonium base used is trimethyl benzyl ammonium hydroxide.

4. A process according to claim 1, wherein the quaternary ammonium base used is trirnethyl phenyl ammonium hydroxide.

5. A process according to claim 1, wherein the hydrodimerization is performed at a temperature of between 10 and C.

6. A process according to claim 1, wherein the hydrodimerization is performed at a temperature of about 0 C.

References Cited UNITED STATES PATENTS 3,534,078 10/1970 Woodhall et a1 260-431 3,591,622 7/1971 Woodhall 260--465.8A

JOSEPH P. BRUST, Primary Examiner US. Cl. X.R. 

